In Volume 9, Number 1 (2008) of the journal High Altitude Medicine & Biology, published by the International Society for Mountain Medicine, Bengt Kayser, Ronald Hulsebosch, and Frank Bosch report a randomized controlled study of the acetylsalicylic acid (aspirin) analog, calcium carbasalate, compared with a placebo and acetazolamide (Diamox) during a rapid ascent of Mount Kilimanjaro (5896 meters or 19,344 feet). The dose of calcium carbasalate used was 380 mg per day; the dose of acetazolamide was 500 mg per day. Ascent of Mt. Kilimanjaro is typical of a rapid ascent that does not require technical mountaineering skills, and is undertaken by numerous persons who are neither experienced in high altitude travel nor particularly knowledgeable about high altitude illness.

The results showed that calcium carbasalate did not prevent acute mountain sickness (AMS) or headache. A very interesting finding was that more than half the individuals taking acetazolamide developed AMS. This may indicate that the dose taken is not sufficient in general, or perhaps only that the ascent rate was too fast for this (or any) dose of acetazolamide to be effective in prevention of AMS. This is even more intriguing, and deserves further investigation, because the trend in recent clinical recommendations has been to use lower doses (e.g., 250 mg per day) of acetazolamide for the purpose of high altitude acclimatization, in order to achieve a beneficial effect while minimizing the side effects. So, it is very important to understand which circumstances of ascent call for a higher dosing regimen.

AMS is a very debilitating disorder, and is likely the harbinger of high altitude cerebral edema (brain swelling). At the very least, it causes headache, poor appetite, fatigue, nausea, and soft tissue swelling, and is markedly disruptive for adventures and recreation at high altitude. This particular study supports our current understanding that non-steroidal antiinflammatory drugs and common analgesics, such as aspirin, ibuprofen, and acetaminophen, are not useful to prevent AMS, and may only serve to mask an important symptom (headache) that indicates when a person is entering a dangerous physiological situation. Of course, if the patient and observers are confident that the headache is mild and that AMS is not progressing, it is reasonable to treat the headache with an analgesic.